Description: (Taken directly from the application) Autosomal dominant polycystic kidney disease (ADPKD) is a slowly progressive renal disorder characterized by the development and steady enlargement of innumerable epithelial cysts that are derived from renal tubules. Proliferation of tubule epithelial cells is an important process in the generation and enlargement of cysts. New evidence indicates that ADPKD cyst epithelial cells may be unusually sensitive to a mitogenic action of cyclic ANT. This project is based on our new findings that cAMP stimulates the in vitro proliferation of ADPKD cyst epithelial cells and that PD98059, a highly selective inhibitor of the mitogen-activated-ERK-pathway, blocks these effects of the nucleotide. By contrast, cells of normal human kidney cortex (HKC) do not proliferate in response to cAMP in vitro. The central thrust of this project is to test the hypothesis that: In ADPKD, renal cyst enlargement is accelerated by elevated levels of intracellular MAP. This nucleotide, through the activation of protein kinase A, stimulates the MAP kinase pathway leading to sustained epithelial mitogenesis and cellular proliferation. The following Specific Aims will test this hypothesis: 1) Epithelial cells from human ADPKD cysts and normal human kidney cortex (HKC), and cAMP sensitive and insensitive strains of NOCK cells will be used to determine the dependence of proliferation on intracellular concentrations of cAMP and the role of apoptosis in the overall proliferative response; 2) Determine the level of involvement of ERK 1,2, MEK and Raf-I in the cAMP-mediated increase in proliferation of responsive renal epithelial cells; 3) Determine the involvement of Rap-I and B-Raf in cAMP-mediated increase in proliferation of responsive renal epithelial cells; 4) Determine if changes in intracellular cAMP levels in situ alter the rate of disease progression in Han: SPRD rats and CD1 pCY mice with inherited forms of PKD. Achievement of these aims requires application of the techniques of molecular biology, cell biology, biochemistry, pharmacology and cellular and integrative physiology. These studies will yield new insights into the molecular mechanisms governing the enlargement of renal cysts and provide a framework for the design of therapeutic measures to combat the progressive destruction of renal parenchyma by cysts.